1. Field of the Invention
The invention relates to the field of lighter-than-air vehicle docking system, and, in particular, to mooring towers for such vehicles.
2. Description of Related Art
There are basically two types of Lighter-than-air vehicles; rigid or non-rigid. There are three general types of non-rigid vehicles: those comprising a single gas filled bag; several gas bags joined together in series; and, of course, those having a multiple number gas bags within a non-rigid envelope. Rigid airships have an internal structure defining the shape of the vehicle and contain a plurality of gas bags therein and with an outer aerodynamic cover there over. In non-rigid designs the cargo flight station and cargo compartments are suspended from the bottom of the vehicle in what is most often referred to as a gondola. In rigid designs it is also common practice to mount the flight station/passenger and cargo compartments under the gas bag, although many designs integrate them in to the rigid frame of the vehicle.
One of the problems with both rigid and non-rigid lighter-than-air vehicles is their limited ability to station keep and/or maneuver when docking, especially if there are any significant cross-winds. This is due primarily to their large cross-sectional area which makes them sensitive to cross-winds. They are particularly difficult to control if the wind is gusting or when there are significant up or down drafts. In fact, docking has proven to be the most difficult portion of a flight for a lighter-than-air vehicle. Thus the most common docking procedure is moor the vehicle by its nose and let it weather vane.
Additionally, unlike a conventional aircraft, the lift force developed by the gas bag remains when docked. Thus as cargo is unloaded, the net lift force increases. In the past, this increase in the net lift has been absorbed by docking restraints, for example mooring lines. If the cargo weight is very large, the force exerted on the mooring lines becomes large and "station keeping" when docked becomes even more difficult. Therefore, unloading and reloading of cargo sometimes must wait until any winds have sufficiently died down or additional mooring lines must be used to "lock" the vehicle in one position. It is obvious, however, that it is always important to minimize the time spent in such operations.
The docking aspects of the problem was addressed in U.S. Pat. No. 1,119,646 "Device For Landing Or Berthing Airships" by H. V. Schleinitz wherein a rotating platform for docking lighter-than-air vehicles is disclosed. In addition, U.S. Pat. No. 1,867,591 "Dirigible Air Dock" by A. S. Pranke discloses a rail mounted rotating platform. U.S. Pat. No. 1,748,500 "Mooring Of Airships by" H. V. Thaden discloses the use of circular tracks having devices for supporting the vehicle such that the vehicle can align with the prevailing wind. U.S. Pat. No. 1,853,777 "Method Of And Apparatus For Berthing Airships" by W. V. N. Powelson, et al. discloses a rotatable suspension system for docking a lighter-than-air vehicle wherein the suspension system is rotated so that it is aligned with the relative wind. After the vehicle is secured the suspension system is rotated such that the vehicle is aligned with a below ground level pit that is used to shelter the vehicle. While all these concepts allow the vehicle to dock and to weather vane after docking; none of the above concepts addresses the problem of making initial contact with the mooring tower.
In the past, when such lighter-than-air vehicles approached the mooring tower, a mooring line in the nose was extended to the ground and hooked up to the top of the tower. A wrench located on either the mooing tower or the vehicle or both were used to reel the vehicle thereto. However, a simple mooring line often proved inadequate because the vehicle would tend to rotate in a vertical plane about the top end of the tower, making it difficult to secure the vehicle to the ground. In addition, mooring the nose of the vehicle and thereafter the rest of the vehicle presents problems in that wind conditions may shift causing the vehicle to rotate about the nose. If the vehicle is near the ground considerable damage may occur. Therefore it is important to secure the nose of the vehicle while it is still a considerable distance above the ground and to thereafter lower the vehicle down while maintaining it in a horizontal attitude by means of mooring lines attached along its entire length. This problem was addressed in U.S. Pat. No. 1,748,500 "Mooring Of Airships" by H. V. Thaden. In the Thaden device, a tower is provided having an extendible arm mounted on the top thereof that can be rotated about the vertical axis of the tower as well as in a vertical plane. A vertical track extends from the top thereof and extends down the side thereof. This track is coupled to the arm and rotates about the vertical axis with the arm. A winch is mounted to the tower that includes a line that extends through the arm that can be coupled to the nose of the airship. The vehicle is first winched to the end of the arm and then lowered down along the track. However, how the vehicle is initially secured to the end of the arm is not disclosed. In addition, the use of a rotating vertical track on a tall tower designed to accommodate a vehicle some 260 feet in diameter would require a massive and expensive structure. Furthermore, no provisions are provided for coupling of the nose of the vehicle to the top in a wind.
Thus it is a primary object of the subject invention to provide a mooring tower for a lighter-than-air vehicle.
It is another primary object of the subject invention to provide a mooring tower that can accommodate extremely large lighter-than-air vehicles.
It is a further object of the subject invention to provide a mooring tower for a lighter-than-air vehicle that includes means to guide the nose of the vehicle to the top thereof.
It is a still further object of the subject invention to provide a mooring tower for a lighter-than-air vehicle that includes means to guide the nose of the vehicle to the top thereof and to thereafter lower the vehicle to the ground.